The subject matter disclosed herein relates generally to multiphase fluid pumps and, more particularly, to a helico-axial pump for pumping a multiphase fluid containing high volumes of gas.
Multiphase fluids, such as gaseous and liquid two-phase fluids exist in many areas of technology, such as oil production. Submersible pumping systems, such as systems that contain helico-axial pumps, are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Most submersible pumping systems include one or more impeller and diffuser combinations, commonly referred to as “stages.” The impellers rotate within adjacent stationary diffusers. During use, the rotating impeller imparts kinetic energy to the fluid. A portion of the kinetic energy is converted to pressure as the fluid passes through the downstream diffuser.
One drawback to the use of submersible pumping systems in the operations involving multiphase fluids, e.g., petroleum-gas mixtures, is the unintended separation of the multiphase fluid into its liquid and gaseous components. This may become particularly severe for multiphase process fluids characterized by a high gas volume fraction. As the multiphase fluid begins to separate into its liquid and gaseous components, the pump becomes vulnerable to “gas locking” Gas locking generally occurs when the multiphase fluids include a significant gas to liquid ratio. The gas-locking phenomenon occurs as the gas bubbles move into low pressure zones of the fluid flow within the submersible pumping system and phase separation may then occur in the flow. Upon phase separation, the gas phase has a tendency to accumulate in certain regions of the flow passages of the pump. If enough gas accumulates in an area of the flow passages of the pump, gas locking occurs preventing the movement of the multiphase fluid. Thus, gas locking causes inefficient and ineffective pump operation and may lead to a decrease in the performance and/or the useful life of the submersible pumping system, such that it may no longer be possible to pump the multiphase fluid effectively.